Elite forces from Iraq's Republican Guard may not be called upon to protect Saddam Hussein in the event of an American attack - for fear that they might turn against him.

The Iraqi leader is determined to keep his crack troops out of Baghdad where their tanks and heavy weaponry could be used to overthrow the regime rather than defend it, the Guardian has learned.

This is because President Saddam cannot be sure of the Guard's loyalties, according to a non-Iraqi source with well-placed contacts in Baghdad. "It's touch and go who they fight for," said the source, who asked not to be identified.

"The officer corps in the Republican Guard are highly trained and motivated, but they hate Saddam Hussein. They also hate the United States. They have a political mind of their own and there's no way Saddam will let them come with their armour into the centre of town."

The United Nations is currently scrambling to devise a means of forcing the Iraqi regime to succumb to renewed arms inspections in a desperate effort to avoid war. Should that fail Iraq has already made clear that its aim is to draw invading US forces into urban warfare, and officials regularly invoke memories of previous city battles in Beirut and Mogadishu.

The result in Iraq, Baghdad strategists calculate, would be to maximise casualties among both the American military and Iraqi civilians, thus increasing the political risks to the US.

But the Republican Guard would not be allowed to join street-fighting inside Bagh dad. Its forces would be kept outside the centre, defending three access routes to the capital, where they would be at the mercy of US bombers.

The Guard, which numbers 50,000-60,000 men, was originally set up as a counterweight to the regular army, and to protect the Iraqi regime, especially the presidential palace in Baghdad. It grew dramatically during the 1980-88 war with Iran, developing a broader role as an elite force.

Although highly privileged and well-equipped in comparison with the regular army, it has become less trusted as a result of several coup plots involving officers from the Guard. One plot, unmasked in 1990, two months before it was due to take place, included a brigadier-general from President Saddam's home town, Tikrit. A member of the Iraqi leader's own tribe was also arrested but later freed.

This led to an expansion of the super-elite Special Republican Guard (SRG), which is now the only major force trusted enough to operate in central Baghdad. Members of the SRG come mainly from areas of Iraq that are noted for their loyalty to President Saddam, including Tikrit. Several of the top officers are drawn from his own family.

The SRG's main function is to protect the Iraqi leader, his relatives and his palaces. Because of the nature of these duties it is more lightly armed than the Republican Guard. The SRG is also much smaller than the Republican Guard, with a normal strength of 12,000-15,000, which can be increased to about 25,000 in emergencies.

Both the Republican Guard and the SRG are under the control of Saddam's younger son, Qusai, rather than the defence ministry, and their members enjoy economic privileges not available to ordinary Iraqis or those in the regular forces.

Various other forces dedicated to intelligence and internal security - possibly totalling more than 100,000 men - could theoretically be deployed in a last-ditch defence of the regime. These include the Special Security Service, the General Intelligence Directorate, the Military Security Service, Military Intelligence and the Border Guards, which all have paramilitary elements.

In addition, there is the Saddam Fedayyeen, a thug militia run by President Saddam's elder son, Udai, which specialises in internal repression - such as cutting off tongues and beheading prostitutes.

Members cover their faces and alternate between white uniforms in summer and black in winter. There is also a youth wing for the under-18s. It is doubtful, however, whether the Fedayyeen's skills would be much use in a full-scale war.

The multiplicity of forces, intended to keep watch on each other and control Iraqi civilians, leads to rivalries and jealousies which are not conducive to a well-coordinated defence of the regime against an external threat.

The conventional army, which probably numbers slightly more than 350,000 (excluding the Republican Guard), is the largest fighting force in the Middle East - but a shadow of its former self. Shortly before the 1991 war it had 955,000 men. That war, followed by 11 years of sanctions, have left it undermanned and poorly equipped, though it could still probably call on 625,000 reservists.

Recent evidence to the US Senate foreign relations committee suggests that at least half of the regular army is at 70% or less of its authorised strength, with some infantry units severely undermanned.

According to the International Institute for Strategic Studies in London ,all army divisions except the Republican Guard are at 50% combat effectiveness

Some infantry units are heavily dependent on conscripts, unlike the Republican Guard, which is a volunteer force. "Six weeks' bombing would finish the conscripts," one analyst said. "They'll not switch to the US but disappear and go home to their mums."

Although the army does have 2,200 tanks - 700 of which are relatively modern -there are reports that much of its equipment is old. According to one American report, half of all army equipment lacks spare parts.

This probably leaves the Republican Guard as the key military player in Iraq, and a potential powerbroker, but doubts about its trustworthiness do not necessarily mean it would switch sides and support the Americans.

Disaffected officers might judge that their interests and special privileges would be better served by pre-empting the Americans and replacing President Saddam with a less controversial leader or at least establishing themselves as a force to be reckoned with by any new regime.

Some in the west argue that disaffection in the Guard can be exploited and encouraged by signalling that any post-Saddam retribution will be limited to the worst elements among them.

"We need to send a message to the Republican Guard that we only want to hit hard-core Tikritis [those closest to Saddam]," says Rosemary Hollis, of the Royal Institute of International Affairs in London.

That would require a careful military strategy aimed at dividing the Guard rather than simply hammering them.

"How do you send a message by air power?" she continued. "There is not enough political thinking about targeting. For instance, how much thought has gone into choosing targets in terms of desired political outcomes?"

Brigadier Tawfiq al-Yasari, a spokesman for the opposition Military Alliance of exiled officers, also emphasises the importance of communication with the Republic Guard - though he includes the SRG in that, too.

"There has to be a political, strategic plan to approach these people," he says. "Our military council has started a campaign to reach out to them."